(DORCHESTER, Mass.) -- A Boston municipal police officer shot and killed an unidentified 25-year-old man yesterday in Dorchester after the man allegedly drew a gun while fleeing from the cop, according to police.

The man collapsed in the middle of Quincy Street, between Mount Everett and Stanley streets, after he was shot about 3:35 p.m. A brown-handled gun was found next to his body.

Boston police Capt. Robert Dunford said the shooting occurred after a pair of Municipal police officers approached three men who appeared to be smoking marijuana in the Quincy-Stanley Playground, only a few feet from the site of the shooting.

Dunford said one of the men ran, and an officer gave chase.

"As he ran away, he appeared to reach for his waist and to pull something from his waistband," the captain said.

He said the officer shot and killed the man after realizing the man was reaching for a gun.

An ambulance happened to be driving along Quincy Street at the instant of the shooting, and EMTs immediately attempted to resuscitate the man, but he was dead on arrival at Boston Medical Center.

Dunford said the dead man had not been positively identified as of last night. Police only said that the man was 25.

More than two hours after the shooting, police continued to process the crime scene for evidence. The 9mm pistol the man allegedly had been carrying lay in the middle of Quincy Street next to large pool of blood that had streamed down the pavement in rivulets toward Columbia Road.

Dunford said the officer who fired the fatal shot was "very, very upset."

"He's gone to the hospital to be evaluated," Dunford said, adding that the officer's name would not be released last night.

Dunford stopped short of saying the officer's actions were justified, saying, "It's still under investigation."

The Boston police homicide unit is leading the investigation.

Dunford said the police patrols of the playground at Quincy and Stanley streets were in response to neighborhood complaints about hoodlums hanging out there.

He said a gang of young males calling themselves the "Quincy-Mount Everett Bombers" had been terrorizing residents for several months.

"There had been a lot of street robberies and assaults starting in about August," Dunford said. "As a result, we instituted random patrols by (Boston police) District C-11 and the Municipal police."

The Municipal police traditionally have patrolled city property and currently are directed by the Boston police.

An area resident who watched as police worked behind the taped-off crime scene concurred that the playground had become a perilous place in recent months.

"It was bad in there. I have a kid, and I wouldn't take my kid in there. No matter what time of day it was," the man said.

The shooting disrupted hundreds of motorists who regularly use Quincy Street as a handy "cut-through" street between Dorchester and Roxbury.

"What happened down there?" a middle-aged woman asked as she walked out of her well-maintained house and watched one car after another being detoured from Quincy Street onto Bellevue Street.

When informed there had been a shooting, the woman responded, "Oh my. That's going to make my kids bug me to move out of here even more than they do already."

Then she picked up her recycling bin from the curb's edge, moved it to her yard and walked down the street.